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  <div class="section" id="s-django-1-4-21-release-notes">
<span id="django-1-4-21-release-notes"></span><h1>Django 1.4.21 release notes<a class="headerlink" href="#django-1-4-21-release-notes" title="Permalink to this headline">¶</a></h1>
<p><em>July 8, 2015</em></p>
<p>Django 1.4.21 fixes several security issues in 1.4.20.</p>
<div class="section" id="s-denial-of-service-possibility-by-filling-session-store">
<span id="denial-of-service-possibility-by-filling-session-store"></span><h2>Denial-of-service possibility by filling session store<a class="headerlink" href="#denial-of-service-possibility-by-filling-session-store" title="Permalink to this headline">¶</a></h2>
<p>In previous versions of Django, the session backends created a new empty record
in the session storage anytime <code class="docutils literal notranslate"><span class="pre">request.session</span></code> was accessed and there was a
session key provided in the request cookies that didn’t already have a session
record. This could allow an attacker to easily create many new session records
simply by sending repeated requests with unknown session keys, potentially
filling up the session store or causing other users’ session records to be
evicted.</p>
<p>The built-in session backends now create a session record only if the session
is actually modified; empty session records are not created. Thus this
potential DoS is now only possible if the site chooses to expose a
session-modifying view to anonymous users.</p>
<p>As each built-in session backend was fixed separately (rather than a fix in the
core sessions framework), maintainers of third-party session backends should
check whether the same vulnerability is present in their backend and correct
it if so.</p>
</div>
<div class="section" id="s-header-injection-possibility-since-validators-accept-newlines-in-input">
<span id="header-injection-possibility-since-validators-accept-newlines-in-input"></span><h2>Header injection possibility since validators accept newlines in input<a class="headerlink" href="#header-injection-possibility-since-validators-accept-newlines-in-input" title="Permalink to this headline">¶</a></h2>
<p>Some of Django’s built-in validators
(<a class="reference internal" href="../ref/validators.html#django.core.validators.EmailValidator" title="django.core.validators.EmailValidator"><code class="xref py py-class docutils literal notranslate"><span class="pre">EmailValidator</span></code></a>, most seriously) didn’t
prohibit newline characters (due to the usage of <code class="docutils literal notranslate"><span class="pre">$</span></code> instead of <code class="docutils literal notranslate"><span class="pre">\Z</span></code> in the
regular expressions). If you use values with newlines in HTTP response or email
headers, you can suffer from header injection attacks. Django itself isn’t
vulnerable because <a class="reference internal" href="../ref/request-response.html#django.http.HttpResponse" title="django.http.HttpResponse"><code class="xref py py-class docutils literal notranslate"><span class="pre">HttpResponse</span></code></a> and the mail sending
utilities in <a class="reference internal" href="../topics/email.html#module-django.core.mail" title="django.core.mail: Helpers to easily send email."><code class="xref py py-mod docutils literal notranslate"><span class="pre">django.core.mail</span></code></a> prohibit newlines in HTTP and SMTP
headers, respectively. While the validators have been fixed in Django, if
you’re creating HTTP responses or email messages in other ways, it’s a good
idea to ensure that those methods prohibit newlines as well. You might also
want to validate that any existing data in your application doesn’t contain
unexpected newlines.</p>
<p><a class="reference internal" href="../ref/validators.html#django.core.validators.validate_ipv4_address" title="django.core.validators.validate_ipv4_address"><code class="xref py py-func docutils literal notranslate"><span class="pre">validate_ipv4_address()</span></code></a>,
<a class="reference internal" href="../ref/validators.html#django.core.validators.validate_slug" title="django.core.validators.validate_slug"><code class="xref py py-func docutils literal notranslate"><span class="pre">validate_slug()</span></code></a>, and
<a class="reference internal" href="../ref/validators.html#django.core.validators.URLValidator" title="django.core.validators.URLValidator"><code class="xref py py-class docutils literal notranslate"><span class="pre">URLValidator</span></code></a> and their usage in the
corresponding form fields <code class="docutils literal notranslate"><span class="pre">GenericIPAddresseField</span></code>, <code class="docutils literal notranslate"><span class="pre">IPAddressField</span></code>,
<code class="docutils literal notranslate"><span class="pre">SlugField</span></code>, and <code class="docutils literal notranslate"><span class="pre">URLField</span></code> are also affected.</p>
<p>The undocumented, internally unused <code class="docutils literal notranslate"><span class="pre">validate_integer()</span></code> function is now
stricter as it validates using a regular expression instead of simply casting
the value using <code class="docutils literal notranslate"><span class="pre">int()</span></code> and checking if an exception was raised.</p>
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<li><a class="reference internal" href="#">Django 1.4.21 release notes</a><ul>
<li><a class="reference internal" href="#denial-of-service-possibility-by-filling-session-store">Denial-of-service possibility by filling session store</a></li>
<li><a class="reference internal" href="#header-injection-possibility-since-validators-accept-newlines-in-input">Header injection possibility since validators accept newlines in input</a></li>
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